3. LECTURE TARGETS Concept of membrane potential. Resting membrane potential. Contribution of sodium potassium pump in the development of membrane potential. Contribution of sodium and potassium ions in the development of membrane potential.

4. All plasma membranes Have A membrane potential (polarized electrically) i.e., charged

5. Due to a separation to a separation of charges across the membrane membrane

6. membrane potential Is measured in mV

7. Membrane Membrane has no potential ECFICF

8. Membrane Membrane has potential ECFICF

9. Membrane Separated charges responsible for potential Remainder of fluid electrically neutral Remainder of fluid electrically neutral ECF ICF

10. Plasma membrane A resting cell

11. MECHANISM OF DEVELOPING RMP Role of sodium potassium pump Role of sodium ions alone Role of potassium ions alone Combined effects of sodium and potassium ions

12. Effects of sodium-potassium pump on membrane potential. Direct effect indirect effect Coupling is 3k + to 2Na + Establish k + to Na + Concentrations across membrane Membrane more Permeable to K + (80% of RMP) Separates charge (20% of RMP)

13. differences in the concentration) Ionic composition ( differences in the concentration) Plasma membrane Extracellular fluid Intracellular fluid 65 5 15 150

14. ICF ECF (Passive) Na + –K + pump (Active) (Passive) K + channelNa + channel Figure 3.29 Page 92

15. If membrane permeable to K + only: –What are the forces that act on K + ? –When would diffusion of K + stops? –When diffusion stops that is equilibrium potential  The concept of equilibrium potential

16. Nernst equation for calculation of equilibrium potential (E) of any particular ion in isolation E =equilibrium potential for ion in mV C o = the concentration of the ion outside the cell in mM C I = the concentration of the ion inside the cell in mM E=61 log CoCo CICI

17. Nernst equation for calculation of equilibrium potential of K + in isolation E K =equilibrium potential for K + in mV = -90 mV E=61 log 5 150 E=61 log 0.033 E=61x-1.477

19. Plasma membrane ECFICF Concentration gradient for Na + Electrical gradient for Na + E Na + = +60 mV If the membrane is permeable to Na + only 150 mM /l 15 mM/l

20. Nernst equation for calculation of equilibrium potential of Na + in isolation E Na =equilibrium potential for Na + in mV = +60 mV E=61 log 150 15 E=61 log 10 E=61x1

21. Plasma membrane ECF ICF Relatively large net diffusion of K + outward tend to establish an E K + of –90 mV No diffusion of A– across membrane Relatively small net diffusion of Na + inward neutralizes some of the potential created by K + alone Resting membrane potential = –70 mV (A – = Large intracellular anionic proteins)

22. At rest neither K + nor Na + are at equilibrium. There is continuous leakage of K + to outside and of Na + to inside, But the concentration gradient is maintained through continuous activity of Na + - K + pump which exactly counterbalances the effect of diffusion of ions. RMP remains constant: passive forces = active forces At resting membrane potential

23. ICF ECF (Passive) Na + –K + pump (Active) (Passive) K + channelNa + channel Figure 3.29 Page 92

24. Mechanisms of RMP Diffusion of K + from inside to outside Na + - K + pump Negatively charged proteins inside

25. Page numbers 75 to 82 Sherwood physiology 7 th edition

26. Message of the day Actions speak louder than words